As an example of an air circulation system that mutually circulates indoor air among a plurality of indoor rooms, there is a technique described in Patent Literature 1, for example. The technique described in Patent Literature 1 is described as being capable of bringing the room temperature of a room with human presence close to the target room temperature thereof by effectively using the heat energy of a room without human presence, and consequently being capable of enhancing the room temperature environment of the room with human presence to a comfortable environment.